Storm water sewer systems are designed for the collection and transport of run-off water from residential and commercial areas to collection basins or repositories such as streams, rivers, lakes, reservoirs and the like. Systems of this type generally comprise a number of drain inlets, typically located along streets, highways, parking facilities and the like, which lead to a network of underground drain lines. These drain lines, in turn, feed the collected run-off water into a particular collection basin.
Unlike sewage systems which deliver waste water to treatment plants, storm water sewer systems transport the run-off water directly to a repository such as a lake, pond or river which often comprises the source of drinking water for nearby communities. Unfortunately, petroleum products such as oil, grease and gasoline, as well as pollutants including heavy metal particles, and, T.C.B. and P.C.B. residues, are carried into the storm water sewer system with the run-off water. In conventional storm water sewer systems, no treatment or removal of these contaminants is provided at any point in the system.
In addition to contaminants such as petroleum products, debris in the form of sand, clay, silt, gravel, stones, small sticks and the like are carried with the run-off water through the drain inlets and into the storm sewer drain pipes of conventional systems. If sufficient debris accumulates within the drain pipes, the volume of run-off water which can be accommodated is correspondingly reduced. In some instances, localized flooding can result in severe rainstorms because the clogged drain lines are unable to carry sufficient volume of run-off water to keep up with the storm.
One solution to the problems outlined above is a removable storm drain cartridge of the type disclosed in U.S. Pat. No. 5,297,367 to Sainz. This "drainage cartridge" is a self-contained unit mounted in the drain inlets of storm water sewer systems for the purposes of collecting debris and petroleum-based pollutants before they can enter the drain pipes. The drain cartridge is a two piece construction including an outer housing, and a separate, inner housing removably mounted within the outer housing. The outer housing has a peripheral lip which is adapted to rest atop a concrete flange formed at the mouth of the drain inlet to support the entire unit therein. Run-off water enters the interior of the unit, flows through the inner housing and then exits the unit through outlet openings formed near the top of the outer housing. In the course of passage through the inner and outer housings, debris such as sand, stones, gravel or the like settles onto the bottom of the outer housing so that it is not carried to the drain pipes below. Additionally, a filter element is mounted at the mouth of the unit to collect petroleum-based contaminants before they are carried away with the run-off water.
Although the '367 patent provides an improvement to existing storm water sewer systems, its design and construction make it impractical and uneconomical for use on a commercial basis. As noted above, a peripheral lip formed on the outer housing of such unit rests atop a concrete flange at the mouth or entrance of the drain inlets in order to mount the unit in place. It has been found that in many localities the drain inlets to the storm water sewer systems are not uniform in size. This typically results from construction of systems during different time periods, by different contractors, and other factors. In any event, it is not economically feasible to construct a large number of different units of the type disclosed in the '367 patent in order to fit all of the varying sizes of drain inlets which may be encountered in a particular locality.
In addition to non-uniformity in dimension, the drain inlets of storm water sewer systems very often have a concrete flange which is uneven along its top surface. Consequently, gaps are formed between the top surface of the concrete flange and the bottom surface of the peripheral lip on the outer housing of the '367 device. Moreover, a peripheral space is nearly always present between the peripheral edge of the lip of the outer housing and the concrete flange due to loose tolerances therebetween which are necessary in order to allow the units to fit within the drain inlets. These gaps and peripheral spaces formed between the unit and the concrete flange provide flow paths, particularly for lower flow rate runoff, directly into the storm water sewer pipes instead of through the unit. As a result, an appreciable amount of runoff may not be filtered, or the debris collected therefrom, with the unit disclosed in the '367 patent.
Another disadvantage of the '367 unit involves its failure to allow for overflow of runoff into the storm water sewer system. As noted above, the peripheral lip on the outer housing of the '367 unit rests directly on the concrete flange at the mouth of the drain inlet. No space or opening of any kind is provided from the mouth of the drain inlet, past the unit to the drain pipes of the storm water sewer system. This can create a serious overflow problem in the adjacent streets, parking areas and the like when the unit becomes blocked or obstructed by debris accumulated within the unit; obstructions at the entrance to the unit such as bags, dead animals and the like; and/or freezing of the water inside of the unit in northern climates. In any of these situations, runoff is prevented from flowing past the unit in the '367 patent and directly into the storm water drain pipes. Instead, the runoff pools at the entrance to the drain inlet and beyond, creating a potentially hazardous situation for motorists, pedestrians and others.
A still further limitation of the '367 device is that it is fabricated in two pieces, including an outer housing and inner housing as noted above. The provision of dyes, molds or other fabricating equipment to make two individual housing sections adds substantial expense to the overall cost of the drainage cartridge. In fact, each unit must be made by hand, and comparatively high-priced materials are employed such as glass reinforced polyester. Additionally, this construction is more difficult to fabricate since tolerances must be met in order for the two housing sections to fit properly together, and within the drain inlets of the storm water sewer system.